Factors Influencing Growth of Individual Brown Trout in Three Streams of the Upper Midwestern United States

Growth rate variation of three age groups of brown trout, Salmo trutta L., (age-0, 1 and 2, and 3+) was quantified from recaptured, individually tagged brown trout and related to season, stream reach, relative abundance, initial length, and movement to examine factors influencing growth in length in three streams in the Midwestern United States.  Total variation in growth was almost five times greater for age-0 than for age-3+ trout.  Individual trout accounted for about 13% of total variation in age-0 growth, season about 57%, and trout initial length and relative abundance combined, another 2%.  The 2006 age-0 cohort had the fastest growth rates in their second spring and summer (2007) and slowest growth in their first winter (2006-2007).  About 53% of total growth variation of age-1 and 2 trout was accounted for by individual trout, season, initial length and stream reach.  Predicted growth rates indicated strong effects of season and initial length.  A significant interaction between these two factors indicated that, although smaller trout grew faster than larger trout, this length effect was most pronounced in spring and summer.  About 35% of total growth variation of age-3+ trout was accounted for by individual trout and season.  Together, season and individual trout characteristics were identified as the most important factors influencing brown trout growth in these streams.